Chinese Music and Scansion

When I first starting learning Chinese I always wondered whether or not tones were somehow incorporated into singing and lyric/melody writing. I later got told that they had no relation. I have since been asked this question a few times and now I'm starting to reconsider.

When talking about music, one might hear a term "scansion" being used. The dictionary definition as found on the internet is "analysis of verse into metrical patterns." My understanding of it is basically how you tie the lyrics and melody together. I sometimes hear my brother commenting on songs saying that they have "bad scansion", which in his case he is usually referring to trying to fit too many words into a line OR when a particular line's melody ascends or descends unnaturally. The second part is what I want to discuss in terms of Chinese.

An example of this in English is the song which my brother uses is Dreams by Fleetwood Mac in the line "When the rain washes you clean, you'll know" on the word "washes". The word is unnaturally emphasized and can sound a little awkward. What made me start considering whether or not this happens in Chinese is when I was listening to 陈奕迅's 一切还好. This song is in Cantonese and Cantonese has 3 flat tones. I was then wondering whether the tones of the words affected the melody or not. I follow the song along with the lyrics with tone markings and it seemed that the tones corresponded pretty well with the melody, but this could just be by chance. I was then thinking would it sound awkward in Chinese to have a melody line where a word like 打击 had the 打 in a high pitch and then 击 in a lower pitch (because a third tone is obviously a lower pitch than a first tone).

Anyone else thought about this? I've written a Chinese song before and want to write more. I was just wondering if there were unwritten rules in terms of Chinese and scansion.